Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
Illumination of a scattering environment (e.g., an environment containing rough surfaces or other scattering objects or features) by a source of coherent, monochromatic light (e.g., a laser) can result in light emitted (i.e., reflected, refracted, diffracted, or otherwise scattered) from the environment forming a speckle pattern. That is, constructive and destructive interference between coherent, monochromatic light that takes different paths through the scattering environment due to scattering by features of the environment, and that thus experiences different path lengths, can form a pattern of light and dark speckles across a surface (e.g., across an array of light sensors). The speckle pattern can be related to the features of the scattering environment, such as the specific geometry of a rough surface and the locations, orientations, and properties of individual scattering objects (e.g., blood cells) in the environment. Additionally, interaction between monochromatic light and scatterers in the environment could cause the wavelength of the scattered light to be different from the wavelength of the illumination by an amount related to the Doppler effect.